Successful implantation is critical for the successful development of the mammalian embryo. Changes in trophoblast cell adhesion play a major role in this process. The experiments proposed here will investigate the role of the cell surface in the differentiation of trophoblast in mouse ectoplacental cones (EPCs) and study the molecular mechanism involved in its interaction with uterine decidual cells. Previous work has indicated that immature trophoblast cell adhesion is mediated in part by the interaction of surface galactosyltransferase (GalTase) with glycoconjugate substrates. Differentiation to non-adhesive, invasive giant cells results in a downregulation of the GalTase adhesion system, although giant cells still possess surface GalTase activity. The experiments proposed here will continue to examine the role of GalTase in implantation. The hypothesis to be tested is that substrate availability for GalTase mediates trophoblast transition from adhesive to migratory behavior by interacting with extracellular substrates to provide a migratory mechanism. These experiments will use existing or newly produced antibodies to study developmental regulation of the cell surface substrate, determine the role of GalTase in migration on defined matrices, and examine the possibility that the enzyme:substrate interaction provides a signal controlling trophoblast differentiation. Implantation will be further studied using a newly developed in vitro model system. Uterine decidual cells will be used as a substrate for the attachment and spreading of EPC trophoblast. These cultures will be analyzed by electron microscopy and the adhesion systems between trophoblast and decidua analyzed with trypsinization, perturbation, and biochemical techniques. Specific antisera will be produced which identifies the molecules involved in trophoblast:decidua interactions. These studies will provide new information on the cellular and molecular mechanism involved in trophoblast differentiation and mammalian implantation. This information can be applied to the development of technologies to assist infertile couples (IVF and embryo transfer) as well as provide new information on the uterine control of tissue invasion. This information could be applied to the study of uncontrolled invasion associated with malignant cell type.